This invention relates to web handling rolls, and, more particularly, to a blotting roller arrangement for preventing contamination of the web drive system by insufficently dried portion of a web.
Numerous products are produced through processes which involve coating a continuous web with a liquid composition, drying the web and subsequently winding up the dried web into a roll for further processing. Depending on the particular path that the web must follow during processing, it may be necessary or expeditious for the web's coated surface to contact rollers which guide the web along a given path. In such processes, it is improtant that the web be completely dried prior to contacting a roller or windup to prevent interroller and/or interweb contamination. If there are portions of the web that have not completely dried, the rollers will be contaminated and will in turn contaminate subsequent sections of the web as they pass over them. In cases where the webs are driven at high speeds, a large portion of the web may become unacceptably contaminated.
This contamination is a particular problem in the production of photosensitive film products, as for instance x-ray film sheets. In such production a web of polyester base is driven past an emulsion coating station where a liquid emulsion layer is coated onto the web. The web is then guided into a dryer, supported only on the uncoated, back side. At the dryer exit it follows a folded path typically through an inspection and accumulator section to a windup station.
In order to obtain the high coating speeds needed in today's competitive environment, it is essential that the coating operation be a continuous uninterrupted process. This is obtained by the use of complex equipment which splices the trailing edge of a web to the leading edge of another without stopping the web and its transport system.
Unfortunately since the splice is thicker than the single web thickness, it disrupts the coating process at the coating station. This disruption occurs because the coating station often comprises a coating head positioned at a very small distance from the web surface which distance may actually be less than the splice thickness. It is therefore necessary to pull the coating head away from the web just before a splice arrives at the coatng station and bring it back into position when the splice has passed through. This process, known as skip-in skip-out, breaks the coating bead between the coating head and the web. Until the head is reestablished and normal coating resumed, a heavier layer tends to be deposited on the web.
Since dryers are designed with a capacity adequate to dry the normal coating to the desired dryness, the heavier web coating due to the skip-in skip-out operation often is insufficiently dried. Some known methods to alleviate this problem are the use of a suction device adjacent the coating head which acts as a vacuum cleaner on demand to suction off excess fluid from the web surface. This, however, requires the placement of extraneous equipment near the coating station, where room is usually at a premium. Additionally, the suction tube must be cleaned after each operation to assure that there are no lingering specs of coating material which may dry out and impede the suctioning system. In the alternative, the drying capacity of the dryer may be increased to handle the excess material on the web. However, this is inefficient and can lead to excessive drying of the normal coating if not properly readjusted.
There is a need for a practical way to avoid contamination of the rollers in a web drive system downstream of a coating station.